Thin layers of cement-based adhesives used to adhere materials such as ceramic tiles to a substrate have been used for a long period of time. These adhesives are sometimes called thin set adhesives. Cement-based adhesives work well when both the substrate and adherent are inorganic materials such as masonry structures, stone, brick, tile, concrete surfaces, etc. However, when either the adherend, substrate, or both are cellulosic materials such as wood, these cement-based adhesive form bonds which are substantially less effective. There have been numerous attempts to improve thin set adhesive to cellulosic substrate bonds. One major improvement has been latex modified cement (thin set) mortars in which a polymeric latex material is added to the cement powder. These mortars are used for the installation of ceramic tiles to a variety of substrates including wallboard, plywood, concrete, etc.
Cement hydrates to form a strong solid mass. This hydration continues for a long period (upwards of 2 years). During this process latex modified mortars tend to lose some of their adhesion and flexibility. As the cement continues to harden, these latex modified thinsets tend to lose some of its peak adhesion and flexibility. Peak adhesion and flexibility peak adhesion and flexibility usually occur around 14 to 28 days.
Additionally, the building industry has moved toward the use of solid body vitreous, porcelain or glass tile. These impervious tiles are significantly harder to bond because of their low absorption rates and smooth vitreous surfaces. While latex modified thinset mortars do adhere to those non-porous tiles, the resulting bond is of low quality and can fail under shear stresses.
However, even these modified thin set adhesives suffer from the poor quality of the adhesive bond between the cement-based adhesive mass and the cellulosic and non-porous substrates. A particular problem with this type of installation has been job failures over plywood and vitreous tile failures. Ceramic tile tends to fail adhesively to (in particular) plywood substrates because of a number of problems, but most often related to substrate movement or simply poor adhesion to the plywood.
Therefore, a modified cement-based adhesive is needed which can effectively bond to cellulosic and non-porous materials such as wood, wallboard and vitreous or glass tiles.